- Email: [email protected]
Formation of thin superconducting YBaCuO layers by oxygen implantation
,~
m
PHYSICA ©
~
ELSEVIER
Physica C 282-287 (1997) 589-590
Formation of thin superconducting YBaCuO layers by oxygen implantation V.Y.Bazarov, Y.Yu.Petukhov, I.A.Faizrakhmanov, G.G.Gumarov, V.A.Shustov, E.P.Zheglov, Y.A.Zhikharev, I.B.Khaibullin Physical-Technical Institute, Sibirsky Trakt, 10/7, Kazan, 420029, Russia Thin superconducting YBaCuO layers have been formed. by using oxygen implantation. Initial monocrystaIline tetragonal YBa2Cu30x (x=6.0-6.1) films 100-150 nm thick were produced by magnetron deposition on SrTi03 or Ah03 substrates. They were implanted with 40keV 0+ ions up to the fluence of 6x10 16cm-2 at the sample temperature ranging from 20 to 650°C. Samples were covered with a blanket of a,-C or MgO. The onset of a superconducting transition in synthesized samples was up to 87K.
1. INTRODUCTION
Ion implantation is an efficient and controlled technique for doping the near-surface region of high temperature superconductors. However, an ion implantation damage was found to destroy superconductivity in YBaCuO thin films [1,2). Nevertheless, Nastasi et.aI. [3J managed to turn BF2-Cu films into a superconducting phase by implanting yttrium ions followed by annealing. superGrigoriev et.aI. [4J synthesized a conducting layer by Cl implantation into tetragonal ceramics YBaCuO. This paper reports on the formation of a thin superconducting YBaCuO layer by 0+ implantation into an oxygen deficient monocrystaIline film.
an irradiation at elevated temperatures. To prevent outdiffusion a part of samples was covered with protective a,-C or MgO films created by an ionbeam assisted deposition. Then, the samples were implanted with 40keV 0+ ions up to the fluence of 6 x 10 16 cm-2. A sample temperature might both vary from 20 to 650°C and keep constant during implantation. For tracking the structure change in the YBaCuO film we chose to observe the position of the (005) and (0011) peaks in X-ray diffraction (XRD) spectra obtained by using Fe Ku. irradiation. The composition of the investigated structure was determined by Auger-electron spectroscopy (AES). The superconductor transition was registered by recording the changes in the ultra high frequency absorption (UHF A) spectrum using EPRradiospectrometer Varian E-12.
2. EXPERIMENTAL YBaCuO monocrystaIline films were grown on SrTi03 or zr02/Ah03 substrates up to a nominal thickness of 120nm by rf magnetron deposition. In «as-deposited» samples the Tc temperature was, typically, 89-90K. Samples were annealed at standard conditions to turn the films into a nonsuperconducting state. Thin YBaCuO films are a very unstable system. This instability is mainly due to an outdiffusion of oxygen especially under
3. RESULTS AND DISCUSSION Two problems must be solved to synthesize superconducting layers during ion implantation. One is connected with annealing of radiation defects, the other - with oxygen outdiffusion. Fig.l demonstrates effectiveness of protective properties of MgO coating against oxygen outdiffusion off orthorhombic YBaCuO film.
This work was partially supported by International Science and Technology Center, Grant No.l30. 0921-4534/97/$17.00 © Elsevier Science B.V All rights reserved. PH S0921-4534(97)00395-X
v.v. Bazarou et aU Physica
590
o
~--~----~--~--~~~
46
47
48 49 50 Bragg angle, 2*8
51
C 282-287 (1997) 589-590
surface region was also observed after implantation with high fluences (D > 3 x 10 16cm- 2). So for the formation of thin superconducting YBaCuO layers by oxygen implantation into tetragonal oxygen-deficient samples certain conditions are to be fulfilled. Oxygen ions with 40 keY must be implanted through a protected 30nm thick films at sample temperature of 400°C, the -2 F·Ig. 2 represent s . 3x 10 16cm. fluence not exceeding the element distribution in a such sample.
Figure l. Fragments of XRD spectra for sample, annealed at 400°C for 110 min (a - without coating, b - covered with 30nm MgO film).
One part of the sample was covered with a protective MgO film, whereas the other part remained unprotected. Then, the sample was annealed at 400°C for 110 min in vacuum. For the protective part the (OOS) peak located at 28 = 48.9So corresponded to the orthorhombic phase with an oxygen content of 0 69 . For the unprotected part of the sample the (OOS) peak shifted to an angle of 28 = 48.43° that corresponds to the tetragonal phase with an oxygen content of 0 61 . Experiments show that for the covered samples the oxygen loss vs. annealing temperature is rather slight up to SSOoC. Moreover, the protective properties of MgO films are high and constant while decreasing thickness down to 30nm, the protective properties of MgO being noticeably higher than that of a-C. To avoid a generation of strong radiation damages, the samples were heated during implantation. However, McCallum et al. [S] report that a structural disorder induced by oxygen implantation can result in significant changes in the near surface composition of the material during subsequent thermal annealing. Furthermore, our investigation show that a high sample temperature (T>400°C) during implantation leads to a significant additional redistribution of elements, e.g. at T=SOOoC Ba atoms segregate to the interface with MgO film, Cu - profile shifts to the depth of the YBaCuO film, and the film is oxygen deficient. Similar decomposition in the near -
Figure 2. Distribution of elements obtained from AES in MgO(30nm)NBaCuO implanted with oxygen (D = 3 x 10 16cm-2, T = 400°C).
The onset of the superconducting transition in the synthesized layers measured by UHF A exceeded the temperature of 87K.
REFERENCES 1. G.lClark, A.D.Marwick, RH.Koch and RB.Laibowitz, Appl.Phys.Lett.,SI(l987)139. 2. G.lClark, F.K.LeGoues, AD.Marwick, RB.Laibowitz and RH.Koch, Appl.Phys.Lett.,SI(1987)1462 3. M.Nastasi, lRTesmer, M.G.Hollander, IF.Smith and C.J.Maggiore, Appl.Phys.Lett.,S2(1988)1729. 4. L.S.Grigorjev, v.Yu.Petukhov, Yu.I.Talanov, G.B.Teitelbaum, I.B.Khaibullin, V.AShustov and AM.Ionov, Sverkhprovodimost 4(1991 )797(in Russian). S. lC.McCallum, C.W.White and L.ABoatner, Mat.Lett.6(l988)374 .
m
PHYSICA ©
~
ELSEVIER
Physica C 282-287 (1997) 589-590
Formation of thin superconducting YBaCuO layers by oxygen implantation V.Y.Bazarov, Y.Yu.Petukhov, I.A.Faizrakhmanov, G.G.Gumarov, V.A.Shustov, E.P.Zheglov, Y.A.Zhikharev, I.B.Khaibullin Physical-Technical Institute, Sibirsky Trakt, 10/7, Kazan, 420029, Russia Thin superconducting YBaCuO layers have been formed. by using oxygen implantation. Initial monocrystaIline tetragonal YBa2Cu30x (x=6.0-6.1) films 100-150 nm thick were produced by magnetron deposition on SrTi03 or Ah03 substrates. They were implanted with 40keV 0+ ions up to the fluence of 6x10 16cm-2 at the sample temperature ranging from 20 to 650°C. Samples were covered with a blanket of a,-C or MgO. The onset of a superconducting transition in synthesized samples was up to 87K.
1. INTRODUCTION
Ion implantation is an efficient and controlled technique for doping the near-surface region of high temperature superconductors. However, an ion implantation damage was found to destroy superconductivity in YBaCuO thin films [1,2). Nevertheless, Nastasi et.aI. [3J managed to turn BF2-Cu films into a superconducting phase by implanting yttrium ions followed by annealing. superGrigoriev et.aI. [4J synthesized a conducting layer by Cl implantation into tetragonal ceramics YBaCuO. This paper reports on the formation of a thin superconducting YBaCuO layer by 0+ implantation into an oxygen deficient monocrystaIline film.
an irradiation at elevated temperatures. To prevent outdiffusion a part of samples was covered with protective a,-C or MgO films created by an ionbeam assisted deposition. Then, the samples were implanted with 40keV 0+ ions up to the fluence of 6 x 10 16 cm-2. A sample temperature might both vary from 20 to 650°C and keep constant during implantation. For tracking the structure change in the YBaCuO film we chose to observe the position of the (005) and (0011) peaks in X-ray diffraction (XRD) spectra obtained by using Fe Ku. irradiation. The composition of the investigated structure was determined by Auger-electron spectroscopy (AES). The superconductor transition was registered by recording the changes in the ultra high frequency absorption (UHF A) spectrum using EPRradiospectrometer Varian E-12.
2. EXPERIMENTAL YBaCuO monocrystaIline films were grown on SrTi03 or zr02/Ah03 substrates up to a nominal thickness of 120nm by rf magnetron deposition. In «as-deposited» samples the Tc temperature was, typically, 89-90K. Samples were annealed at standard conditions to turn the films into a nonsuperconducting state. Thin YBaCuO films are a very unstable system. This instability is mainly due to an outdiffusion of oxygen especially under
3. RESULTS AND DISCUSSION Two problems must be solved to synthesize superconducting layers during ion implantation. One is connected with annealing of radiation defects, the other - with oxygen outdiffusion. Fig.l demonstrates effectiveness of protective properties of MgO coating against oxygen outdiffusion off orthorhombic YBaCuO film.
This work was partially supported by International Science and Technology Center, Grant No.l30. 0921-4534/97/$17.00 © Elsevier Science B.V All rights reserved. PH S0921-4534(97)00395-X
v.v. Bazarou et aU Physica
590
o
~--~----~--~--~~~
46
47
48 49 50 Bragg angle, 2*8
51
C 282-287 (1997) 589-590
surface region was also observed after implantation with high fluences (D > 3 x 10 16cm- 2). So for the formation of thin superconducting YBaCuO layers by oxygen implantation into tetragonal oxygen-deficient samples certain conditions are to be fulfilled. Oxygen ions with 40 keY must be implanted through a protected 30nm thick films at sample temperature of 400°C, the -2 F·Ig. 2 represent s . 3x 10 16cm. fluence not exceeding the element distribution in a such sample.
Figure l. Fragments of XRD spectra for sample, annealed at 400°C for 110 min (a - without coating, b - covered with 30nm MgO film).
One part of the sample was covered with a protective MgO film, whereas the other part remained unprotected. Then, the sample was annealed at 400°C for 110 min in vacuum. For the protective part the (OOS) peak located at 28 = 48.9So corresponded to the orthorhombic phase with an oxygen content of 0 69 . For the unprotected part of the sample the (OOS) peak shifted to an angle of 28 = 48.43° that corresponds to the tetragonal phase with an oxygen content of 0 61 . Experiments show that for the covered samples the oxygen loss vs. annealing temperature is rather slight up to SSOoC. Moreover, the protective properties of MgO films are high and constant while decreasing thickness down to 30nm, the protective properties of MgO being noticeably higher than that of a-C. To avoid a generation of strong radiation damages, the samples were heated during implantation. However, McCallum et al. [S] report that a structural disorder induced by oxygen implantation can result in significant changes in the near surface composition of the material during subsequent thermal annealing. Furthermore, our investigation show that a high sample temperature (T>400°C) during implantation leads to a significant additional redistribution of elements, e.g. at T=SOOoC Ba atoms segregate to the interface with MgO film, Cu - profile shifts to the depth of the YBaCuO film, and the film is oxygen deficient. Similar decomposition in the near -
Figure 2. Distribution of elements obtained from AES in MgO(30nm)NBaCuO implanted with oxygen (D = 3 x 10 16cm-2, T = 400°C).
The onset of the superconducting transition in the synthesized layers measured by UHF A exceeded the temperature of 87K.
REFERENCES 1. G.lClark, A.D.Marwick, RH.Koch and RB.Laibowitz, Appl.Phys.Lett.,SI(l987)139. 2. G.lClark, F.K.LeGoues, AD.Marwick, RB.Laibowitz and RH.Koch, Appl.Phys.Lett.,SI(1987)1462 3. M.Nastasi, lRTesmer, M.G.Hollander, IF.Smith and C.J.Maggiore, Appl.Phys.Lett.,S2(1988)1729. 4. L.S.Grigorjev, v.Yu.Petukhov, Yu.I.Talanov, G.B.Teitelbaum, I.B.Khaibullin, V.AShustov and AM.Ionov, Sverkhprovodimost 4(1991 )797(in Russian). S. lC.McCallum, C.W.White and L.ABoatner, Mat.Lett.6(l988)374 .